Study On The Corrosion Behavior And Microbial Influence For Q235 Steel In Zhoushan Seawater

Microbiologically Influenced Corrosion (MIC) has attracted more and more attention in the recent years. Sulfate Reducing Bacteria (SRB), het-erotrophic bacteria and iron bacteria are the main microbes, which influenced metal corrosion in marine environment. The relationship between the growth of the main microbes that contained in the rust layers of carbon steel exposed in Zhoushan seawater and corrosion rate was studied in this paper. The influence of iron bacteria impacted on corrosion of carbon steel was also studied.The in field corrosion electrochemical detections of metal samples in marine environment have been achieved. The Rp of carbon steel exposed in Zhoushan marine corrosion test station were tested by potentiostatic square wave. The bacterium quantity of SRB, het-erotrophic bacteria and iron bacteria contained in the rust layers of carbon steel which generated with different exposed time in Zhoushan seawater were detected. The weight losses of the carbon steel samples were obtained after corrosion product stripping. The results show that the bacterium quantity was mainly influenced by temperature of the seawater. With the temperature increasing, the bacterium quantity increased, which lead to the higher corrosion rate of carbon steel.The existence of microbes in rust layers accelerated the corrosion rate of carbon steel. X-ray diffraction (XRD) test was used to study the rust layers of carbon steel that exposed to seawater for 162 days. The result indicates that the composition in outer rust layer is more complicated than that in the inner rust layer. The main chemical composition of outer layer is Fe2O3, and the main composition of inner layer is Fe3O4. The rust layers of carbon steel exposed to seawater for 222 days were studied by EDS test. S element contains in the rust layers, and the element content of S in inner rust layer was twice higher than that in outer rust layer. Sulfides were the main metabolism product of SRB, so the result shows that SRB mainly existed in inner rust layer.Based on the variation tendency of Rp and Ecorr of carbon steel in seawater added with iron bacteria, the corrosion results show that the iron bacteria accelerated the corrosion rate of carbon steel, because Fe2+ was oxidized to Fe3+ which promoted the anodic reaction of carbon steel corrosion in iron bacteria's metabolism progress. Iron bacterium also can accelerate the corrosion of carbon steel samples with rust layers. But it has little effect on the Ecorr of carbon steel.